This invention relates to a vacuum pump.
It is known to combine a plurality of rotary vacuum pumps or to combine a plurality of reciprocating vacuum pumps for attaining a high degree of vacuum. However, there are shortcomings that, in the former, it is required to connect in series a multiple number of rotary vacuum pumps for obtaining desired high vacuum because of airtightness or leakage which complicates the construction and, in the latter, there is a problem of a mist of lubricating oil for the reciprocating type vacuum pump entering the stage of high vacuum.